In this work, the strontium-doped lanthanum manganite- a ceramic material- used as cathode in solid oxide fuel cells. An impression of grinding time on the structural and thermal properties of Sr-doped LaMnO3 system with La1-xSrxMnO3 (x=0.2) stoichiometric ratio was investigated. The nano crystallite LSM powder with cubic structure was prepared by varying the milling time of planetary monomill during the mechanochemical method. XRD diffraction patterns confirmed that increasing milling time has effect on phase structure, sintering and thermal behavior of LSM. The optimum sintering temperature was determined and then thermal treatments were investigated with Differential Thermal Analysis (DTA) and Thermal Gravimetric Analysis (TGA) methods, respectively. The results of this research certainly indicated that by increasing grinding time as an important factor in LSM mechanochemical synthesis, the nanocrystallite size and distribution as well as thermal characteristics will be modified.